The nuclear fuel assemblies are formed by assembling rods with a small diameter relative to their length. These rods, of which there are 200 to 300 per assembly, are formed by sheaths filled with nuclear fuel pellets, for example MOX.
These assemblies have a rectangular section of several tens of centimeters per side and measure several meters long.
Each nuclear reactor must be stopped periodically to replace some of the spent fuel assemblies with new fuel assemblies.
The new fuel assemblies are generally made in a pellet manufacturing plant and must be transported to the nuclear plants, where they will be placed in a storage facility before being transferred into the reactors.
The transport of these assemblies between the production plant and the nuclear power plant is done using a cask that includes slots in each of which a new fuel assembly is placed.
Upon arrival at the nuclear power plant, the new fuel assemblies are unloaded from the cask and brought into the storage facility made up of a storage pool, situated near the core of the reactor and in most cases at a level higher than the arrival level of the casks of the assemblies.
The first method for checking the reactivity of a fuel element is its geometry. The handling of a fuel assembly must therefore meet high reliability criteria and in particular show that the consequences of a fall of an assembly are acceptable and do not cause critical accidents or serious environmental consequences.
To date, when the fuel assemblies are transferred from a cask, that cask is moved and brought close to the pool and each assembly is removed from the cask and placed in a pool. This lifting operation of the cask close to the pool then makes it possible to limit the potential fall height of the assembly. The transfer is done either underwater or dry.
In the case of an underwater transfer, the cask is removed from the transport vehicle by suitable lifting means, for example such as a handling crane, and brought into a pool, or an unloading station, attached the storage pool. The related pool is then filled with water, then each fuel assembly is removed from its slot using lifting means and placed in the storage pool. The movement of the fuel assemblies is done underwater, thereby providing suitable biological protection for the operators.
This underwater fuel transfer nevertheless has a drawback, since it is next necessary to decontaminate the cask, and that decontamination operation exposes operators to doses of reactivity.
In the case of a dry transfer, as for example described in FR 2 260 169, the cask is removed from the transport vehicle by a lifting carriage supported by a bridge crane, then deposited in an area designed for storage thereof. Next, the fuel assembly is removed from the transport carriage and hoisted in an armored handling container suspended from the lifting carriage and then transported in the pool. Lifting means, for example such as a winch and a gripping handle fastened to the free end of a chain of the winch, make it possible to hoist the fuel assembly inside the handling container. The fuel assembly is also transferred into an inspection area before being placed in the pool.
All of these operations are time-consuming and require human interventions that risk subjecting operators to critical doses.
Furthermore, it is necessary each time to be able to hoist the cask to the level of the storage pool, which involves constraints on the installation of the receiving building and fall risks for the cask during these operations.
Furthermore, the handling container described in the dry unloading device mentioned above does not, however, have every safety guarantee in the event the fuel assembly falls due to the fact that it does not include closing elements at its base, but rather only means for gripping the fuel assembly in the container.
To that end, handling containers or transfer baskets are known that include closing elements at the base and primarily used to unload spent fuel assemblies from a storage area to store them in containers intended to be transported to another location. The closing element is in particular formed by a sliding or pivoting door actuated remotely. This solution is complex to implement due to the fact that it requires an entire mechanism for actuating the sliding or pivoting door.